The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Solenoid actuators can be used to control fluids (liquids and gases), or for positioning or for control functions. A typical example of a solenoid actuator is the fuel injector. Fuel injectors are used to inject pressurized fuel into a manifold, an intake port, or directly into a combustion chamber of internal combustion engines. Known fuel injectors include electromagnetically-activated solenoid devices that overcome mechanical springs to open a valve located at a tip of the injector to permit fuel flow therethrough. Injector driver circuits control flow of electric current to the electromagnetically-activated solenoid devices to open and close the injectors. Injector driver circuits may operate in a peak-and-hold control configuration or a saturated switch configuration.
Fuel injectors are calibrated, with a calibration including an injector activation signal including an injector open-time, or injection duration, and a corresponding metered or delivered injected fuel mass operating at a predetermined or known fuel pressure. Injector operation may be characterized in terms of injected fuel mass per fuel injection event in relation to injection duration. Injector characterization includes metered fuel flow over a range between high flowrate associated with high-speed, high-load engine operation and low flowrate associated with engine idle conditions.
It is known for engine control to benefit from injecting a plurality of small injected fuel masses in rapid succession. Generally, when a dwell time between consecutive injection events is less than a dwell time threshold, injected fuel masses of subsequent fuel injection events often result in a larger delivered magnitude than what is desired even through equal injection durations are utilized. Accordingly, such subsequent fuel injection events can become unstable resulting in unacceptable repeatability. Fuel injectors are often affected by the operating temperature at any given time. Knowledge of the instantaneous operating temperature of the fuel injector can therefore be useful for controlling fuel injection events of the fuel injector. It is known to correlate resistance of an electrical circuit to operating temperature. When activation of the fuel injector is controlled based upon electrical current applied to an electrical coil, it is difficult to estimate the resistance of the electrical coil due to resistance drops that occur in response to transitions in electrical current applied to the electrical coil.